linux-kernel - Re: [RFC] maximum latency tracking infrastructure

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Date:	Fri, 25 Aug 2006 14:54:52 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Arjan van de Ven <arjan@...ux.intel.com>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	linux-kernel@...r.kernel.org, len.brown@...el.com,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC] maximum latency tracking infrastructure

Arjan van de Ven wrote:
> Jesse Barnes wrote:
> 
>> On Thursday, August 24, 2006 10:41 am, Arjan van de Ven wrote:
>>
>>> The reason for adding this infrastructure is that power management in
>>> the idle loop needs to make a tradeoff between latency and power
>>> savings (deeper power save modes have a longer latency to running code
>>> again).
>>
>>
>> What if a processor was already in a sleep state when a call to 
>> set_acceptable_latency() latency occurs? 
> 
> 
> there's nothing sane that can be done in that case; any wake up already 
> will cause the unwanted latency!
> A premature wakeup is only making it happen *now*, but now is as 
> inconvenient a time as any...
> (in fact it may be a worst case time scenario, say, an audio interrupt...)

Surely you would call set_acceptable_latency() *before* running such
operation that requires the given latency? And that set_acceptable_latency
would block the caller until all CPUs are set to wake within this latency.

That would be the API semantics I would expect, anyway.

-- 
SUSE Labs, Novell Inc.
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